1. Field of the Invention
The present invention relates to a thermal transfer recording method and a recording apparatus using the same wherein an ink is transferred from an ink sheet to a recording medium to record an image on the recording medium.
Such thermal transfer recording apparatuses may include, e.g., a facsimile apparatus, an electronic typewriter, a copying machine, and a printer.
2. Description of the Related Art
In general, conventional thermal transfer printers use ink sheets made by applying thermally meltable (or thermally sublimable) inks to base films. Such ink sheet are selectively heated by a thermal head in correspondence with image signals, and the melted or sublimed ink is transferred to the recording sheet, thereby performing image recording. In general, the ink is perfectly and completely transferred in each image recording cycle (e.g., a so-called one-time sheet). Upon completion of one-character or one-line recording, an ink sheet is conveyed by an amount corresponding to a recording length, and a nonused portion of the ink sheet must be located to the next recording position. For this reason, an amount of ink sheet used is increased to result in an increase in running cost of a thermal transfer printer as compared with a conventional thermal printer for recording on a heat-sensitive paper.
In order to solve the above problem, thermal transfer printers as disclosed in U.S. Pat. No. 4,456,392, Japanese Patent Laid-Open No. 58-201686, and Japanese Patent Publication No. 62-58917 are proposed to differentiate a recording paper conveying speed from an ink sheet conveying speed. As described in these prior arts, an ink sheet capable of performing image recording a plurality of times (n times) is known as a so-called multi-print sheet. When this ink sheet is used and recording of a length L is repeated, the conveying length of the ink sheet conveyed upon each image recording cycle or during image recording can be smaller than the length L (i.e., L/n: n&gt;1). Therefore, utilization efficiency of the ink sheet can be increased by n times, and a decrease in running cost of the thermal transfer printer can be expected. This recording scheme is called a multi-print scheme.
In this multi-print scheme, a conveying speed V.sub.P of the recording paper is given by the following equation: EQU V.sub.p =n.multidot.V.sub.I (n&gt;1)
where V.sub.I is the conveying speed of the ink sheet. The value n is closely associated with image recording quality and may often be changed due to a recording speed. A change in value n is required to prevent formation of wrinkles of an ink sheet as in a case wherein equi-speed recording in a copy mode and intermittent recording in the image reception/recording mode are performed in a facsimile apparatus.
In addition, according to the multi-print scheme as described in the above references, the distance of conveyance of the ink sheet with respect to the recording paper is kept unchanged because the number of multi-prints is always fixed. For example, if an ink sheet whose number of multi-print cycles is five is used, a recording density is low if the number of multi-print cycles exceeds 5. Otherwise, the ink sheet is wasted. It is expected that the number of multi-print cycles of a future ink sheet is increased along with technological developments. Strong demand has arisen for developing a thermal transfer printer in which the number of multi-print cycles corresponds to the ink sheet.
There is also a user's need for saving the ink sheet when the recording density of an image can be relatively low. However, no conventional thermal transfer printer can satisfy this need.
Furthermore, in a conventional thermal transfer printer, a ratio of the feed amount of the ink sheet to the feed amount of the recording paper is kept at a given value. For this reason, when a multi-print sheet is used in a recording unit of, e.g., a facsimile apparatus, and the ink sheet almost runs out in the receiving mode, in the worst case, the last page cannot be printed to the end and facsimile reception is disabled. When the ink sheet runs out during reception, a transmission error occurs on the transmitting side. The transmitting side must resend the page subjected to an error, and the receiving side must change the ink sheet.
In the conventional multi-print scheme using the above conventional ink sheet, as described in the above references, the distance of conveyance of the ink sheet with respect to the recording paper is kept unchanged. This indicates that the multi-print count is kept unchanged. For example, if an ink sheet whose number of multi-print cycles is five is used, a recording density is low if the number of multi-print cycles exceeds 5. Otherwise, the ink sheet is wasted although the recording density is increased. It is expected that the number of multi-print cycles of a future ink sheet is increased along with technological developments. Strong demand has arisen for developing a facsimile apparatus using a thermal transfer printer in which the number of multi-print cycles corresponds to the ink sheet. Furthermore, in communication between facsimile apparatuses, the number of multi-print cycles of the receiving facsimile apparatus is often required to be specified by an operator at a transmitting facsimile apparatus in accordance with types of transmitting original.